1. Field of the Invention
The invention relates to integrated-circuit fabrication techniques and, more particularly, the invention relates to a method and apparatus for providing distributed material management and flow control in a fully automated integrated-circuit factory.
2. Description of the Background Art
An integrated circuit factory comprises a plurality of process tools that function together to form a process bay. The factory may contain a plurality of bays that operate to perform various steps to process a semiconductor wafer that, taken together, form a complete integrated circuit on the wafer. Each process bay contains a bay stocker for temporarily storing cassettes of wafers that will be processed by process tools within the bay. Additionally, a bay may include a “mini-stocker” that is used for temporarily storing cassettes that are awaiting transfer from tool-to-tool. A transport agent is used to move cassettes from stocker-to-tool, tool-to-tool, tool-to-mini-stocker, mini-stocker-to-tool, and tool-to-stocker. The transport agent may be one or more robots, a human, or any other device that transports cassettes of wafers from location to location. One example of a stocker is disclosed in U.S. Pat. No. 6,129,496, issued Oct. 10, 2000.
To efficiently produce integrated circuits the stockers, mini-stockers, and tools must be controlled such that the wafer cassettes move through the factory without bottlenecks, deadlocks, or idle tools. Therefore, there is a need in the art for a method and apparatus for providing distributed material management and flow control in fully automated integrated-circuit factories.